Catalyst transfer in a plural bed hydrogenation process

ABSTRACT

The invention relates to a process for the hydrogenation of hydrocarbon feedstocks in a reactor comprising a number of catalyst beds through which fluidized catalyst descends in countercurrent to feed and hydrogen. The invention provides a catalyst transfer system whereby the catalyst is moved in batches from an upper to the next lower bed by an external catalyst transfer pipe provided with an inlet for hydrogen.

United States Patent 1 1 Irvine 1 Jan. 2, 1973 [54] CATALYST TRANSFER INA PLURAL [56] References Cited BED HYDROGENATION PROCESS UNITED STATESPATENTS Z176] Inventor: P P Pyle 2,520,983 9/1950 Wilcox ..208/l56 H111,Wokmg, Surrey, England 2,702,267 2/1955 Keith ..208/156 2,731,394 1/1956Adams et a1 ..208/155 [22] 1971 3,607,725 9/1971 lrvine ..208/25l 11[21] Appl. No.: 118,697

Primary ExaminerHerbert Levine Attorney- Liberman [30] ForeignApplicatlon Priority Data Feb. 27, 1970 Great Britain ..9519/70 [57]ABSTRACT The invention relates to a process for the hydrogena- [52] US.CL -203/ 8/213, tion of hydrocarbon feedstocks in a reactor compris-208/251 H, 23/1 FT, 23/288 S ing a number of catalyst beds through whichfluidized [51] Int. Cl. ..Cl0g 23/06 catalyst descends in countercurrentto feed and [58] Field of Sear h,, 208/155, 156, 157, 251 H, 89;hydrogen. The invention provides a catalyst transfer 23 FT systemwhereby the catalyst is moved in batches from an upper to the next lowerbed by an external catalyst transfer pipe provided with an inlet forhydrogen.

2 Claims, 1 Drawing Figure CATALYST TRANSFER IN A PLURAL BEDHYDROGENATION PROCESS This invention relates to a method and apparatusfor catalyst handling in hydrogenation reactors.

My US. Application Serial No. 810,127 now US. Pat. No. 3,607,725describes a process for the hydrogenation of non-hydrocarbons in crudeor residua feed which comprises passing the crude or residua feed andmake-up hydrogen through a metal removal reactor comprising a pluralityof catalyst beds through which catalyst falls progressively from thetopjof the reactor to the bottom while crude or residua feed andhydrogen are fed upwardly through the catalyst beds in countercurrent tothe catalyst flow and at a velocity to ensure fluidization of thecatalyst.

I have now found in developing the application of the process principlesto crudes or residua as disclosed in us. Application $61. No. 810,127that it is better to handle the catalyst in a stage as a batch, and towithdraw an entire batch in a stage before catalyst transfer betweenstages and addition.

Handling the catalyst transfer of an entire batch of catalyst in a stageovercomes the disadvantage of fluidization which,'with partialwithdrawal and addition, corresponds in that the catalyst beingwithdrawn contains an equilibrium mixture which contains catalyst whichhas been previously added only a short period before as well as catalystwhich has been resident a longer period than the average because of thethorough mixing of the solid catalyst particles of fluidization.

The number of stages is selected so that the catalyst transfer cycleperiod is reasonable and the change in effluent products compositionbetween the withdrawal of a batch of spent catalyst, catalyst transferbetween stages and addition of a conditioned fresh batch of make-upcatalyst is commercially tolerable.

The nature of the hydrogenation reactions assist in minimizing theproduct change as the greater the extent of hydrogenation the less theeffect of an incremental volume of catalyst. For example, for a metalremoval section accomplishing at least 88 per cent desulfurization, 24stageswould represent a practical selection as this number wouldcorrespond to less than 1 per cent change in product composition betweenthe end of a previous cycle and the commencement of a new cycle withfresh catalyst. Batching instead of partial withdrawal with multi-stagesalso assists'in lining out or achieving steady state equilibriumoperations. It is particularly of assistance at the-final stages inorder to ensure higher activity catalyst corresponding to shorterresidence time contacting the least active reactant. The catalysttransfer cycle period would be governed by overall space velocityrequirements which i is dependent upon the feed characteristics andoperating pressure chosen.

The distribution plate for a stage is relatively inexpensive as, unlikefixed beds, its standing design load is greater than its operatingdynamic loading, and no allowance need be made for increased pressuredrag because of depositing, fouling or plugging as in fixed beds aspacking cannot occur under upflow conditions. It has been found that thestages chosen for batch withdrawal also are economical in that the costof the distribution plates are'more than offset by the increasedefficiency in the use of the catalyst. By enabling a low hydrogencirculation rate throughout the reactor, a smaller diameter may be usedthroughout.

Catalyst transfer between stages is readily effected by an apparatus asshown in the accompanying drawing which shows diagrammatically thesystem used for catalyst transfer according to the present invention.

Referring now to the drawing the metal removal reactor is showndiagrammatically in part as l, the section shown having an upper bed 2and a lower bed 3 separated by distributor plate 4. Catalyst iswithdrawn from upper bed 2 by way of catalyst standpipe 5 provided withcatalyst transfer valve 6. Provision is made for interstage hydrogeninjection through line 7. Catalyst enters lower bed 3 by way of inlet 8.Pipe 5 can be provided with cold quench injection for heat removal.

The interstage hydrogen admitted per stage generally is less than 6 percent of the hydrogen consumption. Therefore, the hydrogen injected to astage may be shut off during catalyst transfer without significantlyaffecting the hydrogen available for accomplishing the desired reaction.The external catalyst transfer pipe serves as a convenient point toinject the interstage hydrogen because of its limited amount and becausethe fluidization will accomplish its mixing with other reactants in thestage. The hydrogen injected also serves as an aeration medium so thatbridging in the catalyst transfer pipe is avoided as well as preventingany stagnant area without hydrogen present which could result inincreased coke deposition.

The catalyst transfer valve is relatively simple mechanically asdiscrete catalyst particles are employed (generally larger than 0.6millimeter diameter) and the valve has a low differential pressure, andit is unnecessary to have a bubble tight seal between catalyst transfer.

The catalyst withdrawal at the base of the reactor must be bubble tightand withdrawing the entire batch before closing aids in the operation ofthis valve.

By transferring an entire batch of catalyst, the closing of the catalysttransfer valve and the catalyst withdrawal valve at the base of areactor is facililated.

The selection of stages results in economically sized catalyst additionand transfer vessels. The catalyst transfer piping is relatively smallcompared to the reactor diameter, even though this reactor diametercorresponds under normal cases to a cross sectional feed throughout ofat least 1.5 times as much as the best of commercial practice to date.

Having the catalyst transfer pipes external of the reactor itself doesnot interfere with a uniform flow pattern within the reactor and thefluid-solid disengaging of the lower reactor stage and affords easyaccessibility to the valves whose temperature is lower than the reactoritself which assists in valve life and maintenance.

Mechanical handling of catalyst is practical because of the relativelylarge hydrocarbon feed mass treated per unit mass of catalyst which mustbe handled. For example, the metal removal catalyst make-up ratetypically corresponds for treating residua from Middle Eastern crudes tousing a fresh catalyst make-up rate equivalent to 1 pound of catalystper 4,000 pounds of residua treated. In this respect, the hydrogenationprocess differs from moving bed and fluidized bed catalytic crackingwherein the catalyst sensible heat provides for the endothermic reactionheat required and the mass of catalyst transferred approximates to thatof the hydrocarbon feed.

it has also been found that it is more advantageous to use a letdownflash gas for accomplishing the sulfiding of the batch of additioncatalyst as the increased hydrogen sulfide content is more desirable forsulfiding the addition batch of catalyst, and its increased hydrocarboncontent more effectively presaturates the catalyst and, thereby, furtherminimizes any heat of wetting upon introduction into the reactor. Thissulfiding treatment may be conveniently carried out in the catalystaddition vessel with only minor modifications to facilitate thistreatment.

What I claim is:

1. A process for the hydrogenation of nonhydrocarhens in crude orresidua feed which comprises passing the crude or residua feed andhydrogen through a metal removal reactor comprising a plurality ofcatalyst beds through which catalyst falls progressively from the top ofthe reactor to the bottom while the crude or residua feed is fedupwardly through the catalyst beds in countercurrent to the catalystflow at a velocity sufficient to maintain said descending catalyst in afluidized state and passing the crude or residua hydrocarbon from themetal removal reactor to a separator stage, the temperatures andpressures of said crude or residua feed and said hydrogen being withinthe ranges to effect the hydrogenation of said non-hydrocarbons in thepresence of said catalysts and wherein catalyst transfer between beds iseffected externally of the reactor by way of a transfer pipe having anoutlet from the lower portion of one bed and an inlet to the next lowerbed, said pipe being provided with a valve adapted to close the pipe andan inlet for interstage hydrogen injection.

2. A process as claimed in claim 1 wherein the catalyst transfer pipe isprovided with cold quench injection for heat removal.

2. A process as claimed in claim 1 wherein the catalyst transfer pipe isprovided with cold quench injection for heat removal.